1. Field of the Invention
The invention relates to photosensitive litho elements. More particularly this invention relates to photosensitive elements having a solvent-processable photosensitive layer and a non-photosensitive solvent-soluble dye or pigment containing contiguous layer.
2. Description of the Prior Art
Photosensitive elements are known which are useful as contact speed lithographic films. In assignee's Bratt and Cohen U.S. Application Ser. No. 741,039, filed Nov. 11, 1976, now abandoned there is disclosed a photopolymerizable litho element wherein the photopolymerizable layer has an optical density of at least 3.0 in the visible region of the spectrum and a maximum thickness of 0.015 mm. Such an element can undergo a treatment known as "dot-etching" which is a reduction in the size of or "etching" the halftone dots formed when the element is exposed to actinic radiation through a halftone screen and developed. Such a lithographic element has advantages over silver halide containing materials. The element has some disadvantage, however, in that the presence of pigment or dye in the photopolymerizable layer in the amount required to give an optical density of at least 3.0 can cause an increase in exposure time as well as have an effect on the photopolymerizable layer.
Two layer photopolymerizable photoresist-forming elements are known wherein one of the layer is nonphotosensitive. One such element is described in published Dutch application 74,13916. The Dutch application is silent with respect to photosensitive litho elements which are dot-etchable since there is no disclosure of a thin lower nonphotosensitive layer having a maximum thickness of 0.015 mm containing a quantity of pigment or dye in an amount to provide an optical density in the visible region of the spectrum of at least 3.0